Induction of competing apoptotic and survival signaling pathways in the macrophage by the ribotoxic trichothecene deoxynivalenol

From ribosome to ribotoxins: understanding the toxicity of deoxynivalenol and Shiga toxin, two food borne toxins

Ribosomes that synthesize proteins are among the most central and evolutionarily conserved organelles. Given the key role of proteins in cellular functions, prokaryotic and eukaryotic pathogens have evolved potent toxins to inhibit ribosomal functions and weaken their host. Many of these ribotoxin-producing pathogens are associated with food. For example, food can be contaminated with bacterial pathogens that produce the ribotoxin Shiga toxin, but also with the fungal ribotoxin deoxynivalenol. Shiga toxin cleaves ribosomal RNA, while deoxynivalenol binds to and inhibits the peptidyl transferase center. Despite their distinct modes of action, both groups of ribotoxins hinder protein translation, but also trigger other comparable toxic effects, which depend or not on the activation of the ribotoxic stress response. Ribotoxic stress response-dependent effects include inflammation and apoptosis, whereas ribotoxic stress response-independent effects include endoplasmic reticulum stress, oxidative stress, and autophagy. For other effects, such as cell cycle arrest and cytoskeleton modulation, the involvement of the ribotoxic stress response is still controversial. Ribotoxins affect one organelle yet induce multiple toxic effects with multiple consequences for the cell. The ribosome can therefore be considered as the cellular "Achilles heel" targeted by food borne ribotoxins. Considering the high toxicity of ribotoxins, they pose a substantial health risk, as humans are highly susceptible to widespread exposure to these toxins through contaminated food sources.

Deoxynivalenol hijacks the pathway of Janus kinase 2/signal transducers and activators of transcription 3 (JAK2/STAT-3) to drive caspase-3-mediated apoptosis in intestinal porcine epithelial cells

Deoxynivalenol (DON) can easily injure the intestinal tract, which represents the first barrier against food contaminants. The intestinal toxicity induced by DON was mainly focused on mitogen-activated protein kinase (MAPK) activation, however, the underlying mechanisms by which DON triggers apoptosis by other pathways remain poorly understood. In this study, the Janus kinase 2/signal transducers and activators of transcription 3 (JAK2/STAT-3) pathway was proposed to regulate the intrinsic apoptosis induced by DON and thoroughly investigated in intestinal porcine epithelial cells (IPEC-J2). First, DON was found to be able to efficiently inhibit cell viability and increase the release of lactate dehydrogenase. It could also enhance the activity of the cleaved caspase-3 in a time-dependent manner, accompanied by a loss of mitochondrial membrane potential and an up-regulation of the apoptosis rate. Then, the expression of genes associated with inflammation and apoptosis were investigated. DON increased the expression of IL-6, IL-1β, TNF-α, SOCS3 and Bax, but decreased the expression of Bcl-2 and Bcl-xL. Moreover, we discovered that DON robustly inhibited STAT-3 activity together with the down-regulation of JAK2, Bcl-2 and Bcl-xL, paralleling the increase in p38 phosphorylation. Furthermore, a pharmacological activation of JAK2/STAT-3 alleviated DON induced-apoptosis. Concurrent with the apoptotic pathway, during the initial exposure to DON (first 4 h), a survival pathway involving phosphorylated Erk1/2, Akt, and FoxO1 was also observed. Thus, apoptosis induced by DON was Janus faced: although the survival pathway was activated, the DON-induced apoptotic JAK2/STAT-3/caspase-3 pathway dominated, leading to an imbalance in cell homeostasis. This study provides a novel avenue to comprehensively reveal the pathological mechanisms of DON-induced intestinal disorders, which is promising for future applications to other contaminants in food and feed.

Effect of the mycotoxin deoxynivalenol in combinational therapy with TRAIL on prostate cancer cells

Tumor necrosis factor-related apoptosis-induced ligand (TRAIL) is reported as a promising anti-cancer therapeutic target. Unfortunately, prostate cancer cells (PCa) are partially resistant to TRAIL-induced apoptosis limiting its therapeutic potential. The existing body of knowledge suggests that naturally produced compounds, such as mycotoxin deoxynivalenol (DON), might potentially sensitize cells to TRAIL treatment and improve the efficiency of therapy. Previously, we observed that DON induces oxidative stress and apoptosis in PCa cell lines. Thus we addressed here whether DON can sensitize PCa cells to TRAIL-induced apoptosis. Our data demonstrates that three out of four tested PCa cell lines pretreated with DON increased TRAIL-induced apoptosis detected with flow cytometry. This effect was associated with oxidative stress (LNCaP and DU-145 cell line) and elevated DNA damage (DU-145, LNCaP, and 22Rv1 cell lines). Next, in the animal model we inoculated PC tumor to SCKID mice followed by administration of DON intraperitoneally and/or TRIAL intravenously. During 21 days monitoring of tumor growth, the animals received 7 doses of DON, TRAIL, DON+TRAIL or control injections. No significant reduction in tumor mass was observed after combinational treatment of TRAIL and DON compared to 1 μg/kg of body weight DON treatment alone, which itself decreased the tumor growth. However, despite the lack of the TRAIL + DON effect, DON itself inducing apoptosis is an interesting compound worth investigating in the context of other combination therapies.

Genome-wide transcriptional profiling and functional analysis reveal miR-330-MAPK15 axis involving in cellular responses to deoxynivalenol exposure

Deoxynivalenol (DON) is one of the mycotoxins that is toxic to agricultural environment, which poses high risks to human and farm animal health. Noncoding RNAs have been shown to be crucial regulators of toxicological processes and as promising biomarkers for toxicity monitoring and prevention of mycotoxin contamination. Herein, we characterized genome-wide transcriptional profiling of porcine intestinal epithelial cells upon DON exposure and illustrated a subset of miRNAs and lncRNAs involved in the cellular processes by targeting genes associated with stress responses. A total of 110 differential expression miRNAs and 143 differential expression lncRNAs were identified between the DON exposure and control cell samples. Interactive network analysis showed that miR-330 was one hub noncoding RNA, expression of which was significantly increased upon DON exposure. Functional enrichment analysis indicated that the genes involved in the networks were mainly enriched in the terms of plasma membrane bounded cell projection assembly, mRNA processing, and regulation of mitochondrion organization. Further functional analysis revealed that high expression of miR-330 inhibits the reactive oxygen species production, cell apoptosis, and autophagic flux in cells upon DON exposure. Luciferase assay further indicated that miR-330 could directly target MAPK15. Knockdown of MAPK15 resulted in decreased reactive oxygen species level and cell apoptosis induced by DON, indicating the existence of miR-330-MAPK15 regulatory axis in regulating DON toxicity. Our work shed novel insights into the mode of action of DON at cellular level and indicated the potential of miR-330 as a biomarker for toxicity monitoring of DON contamination, which contributes to the development of effective biomonitoring and prevention strategies to reduce the toxicological effects of DON.

Mycotoxins in food and feed: toxicity, preventive challenges, and advanced detection techniques for associated diseases

Mycotoxins are produced primarily as secondary fungal metabolites. Mycotoxins are toxic in nature and naturally produced by various species of fungi, which usually contaminate food and feed ingredients. The growth of these harmful fungi depends on several environmental factors, such as pH, humidity, and temperature; therefore, the mycotoxin distribution also varies among global geographical areas. Various rules and regulations regarding mycotoxins are imposed by the government bodies of each country, which are responsible for addressing global food and health security concerns. Despite this legislation, the incidence of mycotoxin contamination is continuously increasing. In this review, we discuss the geographical regulatory guidelines and recommendations that are implemented around the world to control mycotoxin contamination of food and feed products. Researchers and inventors from various parts of the world have reported several innovations for controlling mycotoxin-associated health consequences. Unfortunately, most of these techniques are restricted to laboratory scales and cannot reach users. Consequently, to date, no single device has been commercialized that can detect all mycotoxins that are naturally available in the environment. Therefore, in this study, we describe severe health hazards that are associated with mycotoxin exposure, their molecular signaling pathways and processes of toxicity, and their genotoxic and cytotoxic effects toward humans and animals. We also discuss recent developments in the construction of a sensitive and specific device that effectively implements mycotoxin identification and detection methods. In addition, our study comprehensively examines the recent advancements in the field for mitigating the health consequences and links them with the molecular and signaling pathways that are activated upon mycotoxin exposure.

Deoxynivalenol: Mechanisms of action and its effects on various terrestrial and aquatic species

Deoxynivalenol, a type B trichothecene mycotoxin produced by Fusarium species of fungi, is a ubiquitious contaminant of cereal grains worldwide. Chronic, low dose consumption of feeds contaminated with DON is associated with a wide range of symptoms in terrestrial and aquatic species including decreased feed intake and feed refusal, reduced weight gain, and altered nutritional efficiency. Acute, high dose exposure to DON may be associated with more severe symptoms such as vomiting, diarrhea, intestinal inflammation and gastrointestinal hemorrhage. The toxicity of DON is partly related to its ability to disrupt eukaryotic protein synthesis via binding to the peptidyl transferase site of the ribosome. Moreover, DON exerts its effects at the cellular level by activating mitogen activated protein kinases (MAPK) through a process known as the ribotoxic stress response (RSR). The outcome of DON-associated MAPK activation is dose and duration dependent; acute low dose exposure results in immunostimulation characterized by the upregulation of cytokines, chemokines and other proinflammatory-related proteins, whereas longer term exposure to higher doses generally results in apoptosis, cell cycle arrest, and immunosuppression. The order of decreasing sensitivity to DON is considered to be: swine > rats > mice > poultry ≈ ruminants. However, studies conducted within the past 10 years have demonstrated that some species of fish, such as rainbow trout, are highly sensitive to DON. The aims of this review are to explore the effects of DON on terrestrial and aquatic species as well as its mechanisms of action, metabolism, and interaction with other Fusarium mycotoxins. Notably, a considerable emphasis is placed on reviewing the effects of DON on different species of fish.

The toxicity mechanisms of DON to humans and animals and potential biological treatment strategies

Deoxynivalenol, also known as vomitotoxin, is produced by Fusarium, belonging to the group B of the trichothecene family. DON is widely polluted, mainly polluting cereal crops such as wheat, barley, oats, corn and related cereal products, which are closely related to lives of people and animals. At present, there have been articles summarizing DON induced toxicity, biological detoxification and the protective effect of natural products, but there is no systematic summary of this information. In addition to ribosome and endoplasmic reticulum, recent investigations support that mitochondrion is also organelles that DON can damage. DON can't directly act on mitochondria, but can indirectly cause mitochondrial damage and changes through other means. DON can indirectly inhibit mitochondrial biogenesis and mitochondrial electron transport chain activity, ATP production, and mitochondrial transcription and translation. This review will provide the latest progress on mitochondria as the research object, and systematically summarizes all the toxic mechanisms of DON. Here, we discuss DON induced mitochondrial-mediated apoptosis and various mitochondrial toxicity. For the toxicity of DON, many methods have been derived to prevent or reduce the toxicity. Biological detoxification and the antioxidant effect of natural products are potentially effective treatments for DON toxicity.

Does chronic dietary exposure to the mycotoxin deoxynivalenol affect the porcine hepatic transcriptome when an acute-phase response is initiated through first or second-pass LPS challenge of the liver?

The sensitivity of pigs to deoxynivalenol (DON) might be increased by systemic inflammation (SI), which also has consequences for hepatic integrity. Liver lesions and a dys-regulated gene network might hamper hepatic handling and elimination of DON whereby the way of initiation of hepatic inflammation might play an additional role. First and second-pass exposure of the liver with LPS for triggering a SI was achieved by LPS infusion via pre- or post-hepatic venous route, respectively. Each infusion group was pre-conditioned either with a control diet (0.12 mg DON/kg diet) or with a DON-contaminated diet (4.59 mg DON/kg diet) for 4 wk. Liver transcriptome was evaluated at 195 min after starting infusions. DON exposure alone failed to modulate the mRNA expression significantly. However, pre- and post-hepatic LPS challenges prompted transcriptional responses in immune and metabolic levels. The mRNAs for B-cell lymphoma 2-like protein 11 as a key factor in apoptosis and IFN-γ released by T cells were clearly up-regulated in DON-fed group infused with LPS post-hepatically. On the other hand, mRNAs for nucleotide binding oligomerization domain containing 2, IFN-α and eukaryotic translation initiation factor 2α kinase 3 as ribosomal stress sensors were exclusively up-regulated in control pigs with pre-hepatic LPS infusion. These diverse effects were traced back to differences in TLR4 signalling.

Deoxynivalenol Has the Capacity to Increase Transcription Factor Expression and Cytokine Production in Porcine T Cells

Deoxynivalenol (DON) is a Fusarium mycotoxin that frequently contaminates the feed of farm animals. Pigs with their monogastric digestive system are in particular sensitive to DON-contaminated feed. At high concentrations, DON causes acute toxic effects, whereas lower concentrations lead to more subtle changes in the metabolism. This applies in particular to the immune system, for which immunosuppressive but also immunostimulatory phenomena have been described. Research in human and rodent cell lines indicates that this may be partially explained by a binding of DON to the ribosome and subsequent influences on cell signaling molecules like mitogen-activated protein kinases. However, a detailed understanding of the influence of DON on functional traits of porcine immune cells is still lacking. In this study, we investigated the influence of DON on transcription factor expression and cytokine production within CD4⁺, CD8⁺, and γδ T cells in vitro. At a DON concentration, that already negatively affects proliferation after Concanavalin A stimulation (0.8 μM) an increase of T-bet expression in CD4⁺ and CD8⁺ T cells was observed. This increase in T-bet expression coincided with elevated levels of IFN-γ and TNF-α producing T-cell populations. Increases in T-bet expression and cytokine production were found in proliferating and non-proliferating T cells, although increases were more prominent in proliferating cell subsets. Differently, IL-17A production by CD4⁺ T cells was not influenced by DON. In addition, frequencies of regulatory T cells and their expression of Foxp3 were not affected. In γδ T cells, GATA-3 expression was slightly reduced by DON, whereas T-bet levels were only slightly modulated and hence IFN-γ, TNF-α, or IL-17A production were not affected. Our results show for the single-cell level that DON has the capacity to modulate the expression of transcription factors and related cytokines. In particular, they suggest that for CD4⁺ and CD8⁺ T cells, DON can drive T-cell differentiation into a pro-inflammatory type-1 direction, probably depending on the already prevailing cytokine milieu. This could have beneficial or detrimental effects in ongoing immune responses to infection or vaccination.

In-Vitro Cell Culture for Efficient Assessment of Mycotoxin Exposure, Toxicity and Risk Mitigation

Mycotoxins are toxic secondary fungal metabolites that commonly contaminate crops and food by-products and thus, animal feed. Ingestion of mycotoxins can lead to mycotoxicosis in both animals and humans, and at subclinical concentrations may affect animal production and adulterate feed and animal by-products. Mycotoxicity mechanisms of action (MOA) are largely unknown, and co-contamination, which is often the case, raises the likelihood of mycotoxin interactions. Mitigation strategies for reducing the risk of mycotoxicity are diverse and may not necessarily provide protection against all mycotoxins. These factors, as well as the species-specific risk of toxicity, collectively make an assessment of exposure, toxicity, and risk mitigation very challenging and costly; thus, in-vitro cell culture models provide a useful tool for their initial assessment. Since ingestion is the most common route of mycotoxin exposure, the intestinal epithelial barrier comprised of epithelial cells (IECs) and immune cells such as macrophages, represents ground zero where mycotoxins are absorbed, biotransformed, and elicit toxicity. This article aims to review different in-vitro IEC or co-culture models that can be used for assessing mycotoxin exposure, toxicity, and risk mitigation, and their suitability and limitations for the safety assessment of animal foods and food by-products.

Heme oxygenase-1 regulates autophagy through carbon-oxygen to alleviate deoxynivalenol-induced hepatic damage

Deoxynivalenol (DON) cannot be totally removed due to its stable chemical characteristics and chronic exposure to low doses of DON causes significant toxic effects in humans and animals. However, the potential hazard of such low-dose exposure in target organs still remains not completely understood, especially in liver, which is mainly responsible for detoxification of DON. In the present study, we demonstrated for the first time that estimated human daily DON exposure (25 μg/kg bw) for 30 and 90 days caused low-grade inflammatory infiltration around hepatic centrilobular veins, elevated systemic IL-1β, IL-6 and TNF-α and impaired liver function evidenced by increased serum ALT activity. At the molecular level, expressions of autophagy-related proteins as well as Cleaved Caspase-3 and Cleaved Caspase-7 were upregulated during DON exposure, which indicated the activation of autophagy and apoptosis. Importantly, AAV-mediated liver-specific overexpression of HO-1 reversed DON-induced liver damages, upregulated autophagy and attenuated apoptosis in liver, while AAV-mediated HO-1 silence aggravated DON-induced liver damages, inhibited autophagy and increased apoptosis. Furthermore, in vitro experiments demonstrated that lentivirus-mediated HO-1 overexpression in Hepa 1-6 cells prolonged the duration of autophagy and delayed the onset of apoptosis. HO-1 silence in Hepa 1-6 cells inhibited activation of autophagy and accelerated occurrence of apoptosis, and these could be recovered by CO pre-treatment. Therefore, we suppose that HO-1 might be a potential research target to protect human and animal from liver injuries induced by low dose of DON exposure.

Deoxynivalenol Affects Proliferation and Expression of Activation-Related Molecules in Major Porcine T-Cell Subsets

The Fusarium mycotoxin deoxynivalenol (DON) contaminates animal feed worldwide. In vivo, DON modifies the cellular protein synthesis, thereby also affecting the immune system. However, the functional consequences of this are still ill-defined. In this study, peripheral blood mononuclear cells from healthy pigs were incubated with different DON concentrations in the presence of Concanavalin A (ConA), a plant-derived polyclonal T-cell stimulant. T-cell subsets were investigated for proliferation and expression of CD8α, CD27, and CD28, which are involved in activation and costimulation of porcine T cells. A clear decrease in proliferation of all ConA-stimulated major T-cell subsets (CD4⁺, CD8⁺, and γδ T cells) was observed in DON concentrations higher than 0.4 µM. This applied in particular to naïve CD4⁺ and CD8⁺ T cells. From 0.8 μM onwards, DON induced a reduction of CD8α (CD4⁺) and CD27 expression (CD4⁺ and CD8⁺ T cells). CD28 expression was diminished in CD4⁺ and CD8⁺ T cells at a concentration of 1.6 µM DON. None of these effects were observed with the DON-derivative deepoxy-deoxynivalenol (DOM-1) at 16 µM. These results indicate that DON reduces T-cell proliferation and the expression of molecules involved in T-cell activation, providing a molecular basis for some of the described immunosuppressive effects of DON.

The wheat SnRK1α family and its contribution to Fusarium toxin tolerance

Deoxynivalenol (DON) is a mycotoxin produced by phytopathogenic Fusarium fungi in cereal grain and plays a role as a disease virulence factor. TaFROG (Triticum aestivum Fusarium Resistance Orphan Gene) enhances wheat resistance to DON and it interacts with a sucrose non-fermenting-1 (SNF1)-related protein kinase 1 catalytic subunit α (SnRK1α). This protein kinase family is central integrator of stress and energy signalling, regulating plant metabolism and growth. Little is known regarding the role of SnRK1α in the biotic stress response, especially in wheat. In this study, 15 wheat (Triticum aestivum) SnRK1α genes (TaSnRK1αs) belonging to four homoeologous groups were identified in the wheat genome. TaSnRK1αs are expressed ubiquitously in all organs and developmental stages apart from two members predominantly detected in grain. While DON treatment had either no effect or downregulated the transcription of TaSnRK1αs, it increased both the kinase activity associated with SnRK1α and the level of active (phosphorylated) SnRK1α. Down-regulation of two TaSnRK1αs homoeolog groups using virus induced gene silencing (VIGS) increased the DON-induced damage of wheat spikelets. Thus, we demonstrate that TaSnRK1αs contribute positively to wheat tolerance of DON and conclude that this gene family may provide useful tools for the improvement of crop biotic stress resistance.

Deoxynivalenol induces oxidative stress, inflammatory response and apoptosis in bovine mammary epithelial cells

Deoxynivalenol (DON) is a toxic secondary metabolite produced by Fusarium graminearum. It is one of the most common feed contaminants that poses a serious threat to the health and performance of dairy cows. This study investigated the in vitro cytotoxicity of DON on bovine mammary epithelial cells (MAC-T). DON at different concentrations (0.25, 0.3, 0.5, 0.8, 1 or 2 μg/ml) inhibited the growth of MAC-T cells after 24 hr of exposure (p < .001). DON at 0.25 μg/ml increased lactate dehydrogenase (LDH) leakage (p < .05); decreased glutathione (GSH) levels (p < .001), total superoxide dismutase (T-SOD) activity and total antioxidant capacity (T-AOC; p < .01); and increased malondialdehyde (MDA) concentration (p < .01) in MAC-T cells after 24 hr of exposure. We also observed that DON increased reactive oxygen species (ROS) levels in cells incubated for 9, 15 and 24 hr (p < .001). DON at 0.25 μg/ml triggered oxidative damage in MAC-T cells. Furthermore, it induced an inflammatory response in the cells incubated for 9, 15 and 24 hr (p < .05) by increasing the mRNA expression levels of nuclear factor kappa B, myeloid differentiation factor 88 (MyD88), tumour necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-6, cyclooxygenase-2 and IL-8. We further examined the effect of DON on apoptosis. DON prevented normal proliferation of MAC-T cells by blocked cell cycle progression in 24 hr (p < .001). In addition, the apoptosis rate measured using annexin V-FITC significantly increased (p < .05) with increase in the mRNA expression level of Bax (p < .01) and increase in the Bax/Bcl-2 ratio (p < .01) in cells incubated for 24 hr. In summary, DON exerts toxic effects in MAC-T cells by causing oxidative stress, inducing an inflammatory response, affecting cell cycle and leading to apoptosis.

Research Progress on the Toxic Antagonism of Selenium Against Mycotoxins

Animal feed is prone to becoming infected with molds during production and storage, resulting in secondary metabolite mycotoxins, such as aflatoxin B₁ (AFB₁), T-2 toxins, deoxynivalenol (DON), and ochratoxin A (OTA), which are harmful to humans and animals. Selenium is an essential trace element for humans and animals, and it is also an effective antioxidant. Many studies have shown that selenium can reduce the damage caused by mycotoxins in animals. This article reviews the current literature on the antagonistic effects of selenium on AFB₁, T-2, DON, and OTA toxicity.

Induction of Apoptosis and Activation of JNK and p38 MAPK Pathways in Deoxynivalenol-Treated Cell Lines

Deoxynivalenol (DON) is a mycotoxin produced by what are thought to be the most prevalent toxin-producing fungi of the Fusarium genus. Here, we present the results of apoptosis induction, phosphorylation of c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinases (MAPKs), and expression of the c-Jun protein after DON treatment, in a pre-B lymphocyte REH cell line. In addition, human pre-T lymphocyte Jurkat, hamster kidney-derived BHK21 and mouse hepatoma MH-22a cells were used in comparative experiments in vitro. We found that the DON effect was cell origin-dependent and dose-dependent, with a significant slow-down of cell proliferation and increase of apoptotic cells in blood cell lines. BHK21 and MH-22a cells were less sensitive to the DON effect. In blood-derived REH and Jurkat cells, DON-induced apoptotic changes were preceded by an increase in JNK and p38 MAPKs phosphorylation, as well as in c-Jun expression. However, the activation of JNK phosphorylation and c-Jun expression were transient, but did not coincide with each other. An inhibitor of JNK1/2, SP600125, had a negligible negative effect on REH cell viability after DON treatment, demonstrating that JNK does not contribute to DON-induced apoptosis. In contrast, studies on the role of p38 MAPK revealed that p38 signalling is required for DON-induced apoptosis in REH cells.

Exposure of pregnant sows to deoxynivalenol during 35-70 days of gestation does not affect pathomorphological and immunohistochemical properties of fetal organs

In order to evaluate the influence of deoxynivalenol (DON) on histomorphological and immunohistochemical parameters in the development of porcine fetuses, five pregnant sows were fed a control diet (0.15 mg DON/kg diet) and seven sows a contaminated diet (4.42 mg DON/kg diet) between days 35 and 70 of gestation. On day 70, fetuses were delivered by caesarean section and sows and fetuses were euthanized. Tissue samples of three fetuses from each sow were collected, fixed in formalin, and processed routinely for light microscopy and immunohistochemistry. At necropsy, no macroscopic lesions were observed in any organ of the fetuses. Histomorphological, immunohistochemical, and morphometrical parameters of the immune system, liver, and intestinal tract were examined. The following antibodies were used in the liver, spleen, lymph nodes, thymus, gut, and bone marrow to compare control- and DON-treated animals: (I) CD3 and CD79a (T and B lymphocytes differentiation); (II) myeloid/histiocyte antigen 387 (MAC) (identification of macrophages); (III) Ki-67 Antigen (Ki-67) (proliferation marker); (IV) p-p-38 mitogen-activated protein kinases (p-p38 MAPK) as well as caspase-3 (cas3) and caspase-9 (cas9) (enzymes of apoptosis cascade); (V) tumor necrosis factor-alpha (TNFα) (immune-related protein). The results of the study show that exposure of pregnant sows with DON between gestation days 35 and 70 causes no pathomorphologically or immunohistochemically detectable alterations in all fetal organs examined.

Trichothecenes: immunomodulatory effects, mechanisms, and anti-cancer potential

Paradoxically, trichothecenes have both immunosuppressive and immunostimulatory effects. The underlying mechanisms have not been fully explored. Early studies show that dose, exposure timing, and the time at which immune function is assessed influence whether trichothecenes act in an immunosuppressive or immunostimulatory fashion. Recent studies suggest that the immunomodulatory function of trichothecenes is also actively shaped by competing cell-survival and death-signaling pathways. Autophagy may also promote trichothecene immunosuppression, although the mechanism may be complicated. Moreover, trichothecenes may generate an "immune evasion" milieu that allows pathogens to escape host and vaccine immune defenses. Some trichothecenes, especially macrocyclic trichothecenes, also potently kill cancer cells. T-2 toxin conjugated with anti-cancer monoclonal antibodies significantly suppresses the growth of thymoma EL-4 cells and colon cancer cells. The type B trichothecene diacetoxyscirpenol specifically inhibits the tumor-promoting factor HIF-1 in cancer cells under hypoxic conditions. Trichothecin markedly inhibits the growth of multiple cancer cells with constitutively activated NF-κB. The type D macrocyclic toxin Verrucarin A is also a promising therapeutic candidate for leukemia, breast cancer, prostate cancer, and pancreatic cancer. The anti-cancer activities of trichothecenes have not been comprehensively summarized. Here, we first summarize the data on the immunomodulatory effects of trichothecenes and discuss recent studies that shed light on the underlying cellular and molecular mechanisms. These mechanisms include autophagy and major signaling pathways and their crosstalk. Second, the anti-cancer potential of trichothecenes and the underlying mechanisms will be discussed. We hope that this review will show how trichothecene bioactivities can be exploited to generate therapies against pathogens and cancer.

Effect of T-2 toxin-injected shrimp muscle extracts on mouse macrophage cells (RAW264.7)

Following intramuscular injections of 0.1 mL, 3 mg kg^-1BW^-1(1/10 LD₅₀) T-2 toxin (T-2), the tissue concentration of T-2 in shrimp was quantitatively detected using LC-MS/MS. The biological half-time (t_1/2) of T-2 in blood was 40.47 ± 0.24 min. The highest number of intramuscular T-2 shrimp could tolerate when given at blood t_1/2 intervals was 4. The shrimps which were injected 5 T-2 died. The T-2 toxin highest accumulation was 0.471 ± 0.012 ng g^-1BW^-1. The effect of toxic shrimp muscle subjected to different processing conditions (high pressure, trifluoroacetic acid, acid and alkali digestions, artificial digestive juice [to simulate exposure to gastric and intestinal juices]) on mouse macrophage cells (RAW267.4) were evaluated by the MTT assay. The inhibition ratio of 2% muscle extract on RAW267.4 was 85.70 ± 2.63%. The immunocytotoxicity of muscle extracts to RAW264.7 was highest in muscle extracts subjected to physical and chemical digestion (high pressure > NaOH > trifluoroacetic acid > 0.02 M HCl > 0.2 M HCl > controls), and also artificial digestion (artificial intestinal juice > artificial gastric juice > N type intestinal juice > N type gastric liquid > controls). Results showed that high-pressure and artificial intestinal juice were most effective in the release of modified T-2 to free T-2 thus enhancing toxicity. These results can be interpreted as measurement of T-2 in food being of little value because of enhanced toxicity of T-2-contaminated food as they pass through the gastrointestinal tract.

Protective Effect of Saccharomyces boulardii on Deoxynivalenol-Induced Injury of Porcine Macrophage via Attenuating p38 MAPK Signal Pathway

The aims of our study were to evaluate the effects of Saccharomyces boulardii (S. boulardii) on deoxynivalenol (DON)-induced injury in porcine alveolar macrophage cells (PAMCs) and to explore the underlying mechanisms. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, flow cytometric analysis, ELISA, qRT-PCR, and western blot were performed to assess whether S. boulardii could prevent DON-induced injury by p38 mitogen-activated protein kinase (p38 MAPK) signal pathway. The results showed that pretreatment with 8 μM DON could decrease the viability of PAMC and significantly increase the apoptosis rate of PAMC, whereas S. boulardii could rescue apoptotic PAMC cells induced by DON. Further experiments revealed that S. boulardii effectively reversed DON-induced cytotoxicity via downregulating the expression of TNF-α, IL-6, and IL-lβ. In addition, S. boulardii significantly alleviated DON-induced phosphorylation and mRNA expression of p38 and further increased the expression of apoptosis regulation genes Bcl-xl and Bcl-2 and inhibited the activation of Bax. Our results suggest that S. boulardii could suppress DON-induced p38 MAPK pathway activation and reduce the expression of downstream inflammatory cytokines, as well as promote the expression of anti-apoptotic genes to inhibit apoptosis induced by DON in PAMC.

Deoxynivalenol induces toxic effects in the ovaries of pigs: An ex vivo approach

Deoxynivalenol (DON) is a frequently found trichothecene mycotoxin that elicits toxic effects on humans and animals. In pigs, DON induces changes in digestive and immune systems. Effects on the reproductive system are scarce and mainly based in in vitro models. The aim of this study was to evaluate, using an ex vivo model, the effects of DON on the morphology of ovaries of pigs in all stages of follicular development. Six 5-month-old pigs were used for sampling the explants. Thirty-six explants were incubated for 48 hours in culture medium (n = 18) or medium containing 10 μM of DON (n = 18). After the incubation period, the explants were submitted to histologic and immunohistochemical (proliferating cell nuclear antigen [PCNA] expression) analysis. Histologic changes were scored, and a lesional score was established. Oocytes and follicular cells immunostained for PCNA were counted. Explants exposed to DON showed a significant increase in the lesional score (P = 0.0004) compared to control explants. The main histologic changes were degeneration of oocytes and granulosa cells, interstitial edema and pyknotic cells. DON induced a reduction in the number of normal follicles in all stages of follicular development: primordial (P = 0.005), primary (P = 0.04), and growing follicles (P = 0.04) compared to control group. Deoxynivalenol also induced a significant increase (P ≤ 0.05) in the number of pyknotic oocytes in all stages of follicular development; however, no significant change in PCNA expression in oocytes or follicular cells was observed. These results indicated that DON induces toxic effects on the ovaries, affecting follicular development and interfering with reproductive parameters on pigs. Also, the present data indicate that ovarian explants are an adequate model for assessing reproductive toxicity.

Phosphoproteome Analysis Reveals the Molecular Mechanisms Underlying Deoxynivalenol-Induced Intestinal Toxicity in IPEC-J2 Cells

Deoxynivalenol (DON) is a widespread trichothecene mycotoxin that commonly contaminates cereal crops and has various toxic effects in animals and humans. DON primarily targets the gastrointestinal tract, the first barrier against ingested food contaminants. In this study, an isobaric tag for relative and absolute quantitation (iTRAQ)-based phosphoproteomic approach was employed to elucidate the molecular mechanisms underlying DON-mediated intestinal toxicity in porcine epithelial cells (IPEC-J2) exposed to 20 μM DON for 60 min. There were 4153 unique phosphopeptides, representing 389 phosphorylation sites, detected in 1821 phosphoproteins. We found that 289 phosphopeptides corresponding to 255 phosphoproteins were differentially phosphorylated in response to DON. Comprehensive Gene Ontology (GO) analysis combined with Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment revealed that, in addition to previously well-characterized mitogen-activated protein kinase (MAPK) signaling, DON exposure altered phosphatidylinositol 3-kinase/Akt (PI3K/Akt) and Janus kinase/signal transducer, and activator of transcription (JAK/STAT) pathways. These pathways are involved in a wide range of biological processes, including apoptosis, the intestinal barrier, intestinal inflammation, and the intestinal absorption of glucose. DON-induced changes are likely to contribute to the intestinal dysfunction. Overall, identification of relevant signaling pathways yielded new insights into the molecular mechanisms underlying DON-induced intestinal toxicity, and might help in the development of improved mechanism-based risk assessments in animals and humans.

A Novel Zak Knockout Mouse with a Defective Ribotoxic Stress Response

Ricin activates the proinflammatory ribotoxic stress response through the mitogen activated protein 3 kinase (MAP3K) ZAK, resulting in activation of mitogen activated protein kinases (MAPKs) p38 and JNK1/2. We had a novel zak−/− mouse generated to study the role of ZAK signaling in vivo during ricin intoxication. To characterize this murine strain, we intoxicated zak−/− and zak+/+ bone marrow–derived murine macrophages with ricin, measured p38 and JNK1/2 activation by Western blot, and measured zak, c-jun, and cxcl-1 expression by qRT-PCR. To determine whether zak−/− mice differed from wild-type mice in their in vivo response to ricin, we performed oral ricin intoxication experiments with zak+/+ and zak−/− mice, using blinded histopathology scoring of duodenal tissue sections to determine differences in tissue damage. Unlike macrophages derived from zak+/+ mice, those derived from the novel zak−/− strain fail to activate p38 and JNK1/2 and have decreased c-jun and cxcl-1 expression following ricin intoxication. Furthermore, compared with zak+/+ mice, zak−/− mice have decreased duodenal damage following in vivo ricin challenge. zak−/− mice demonstrate a distinct ribotoxic stress–associated phenotype in response to ricin and therefore provide a new animal model for in vivo studies of ZAK signaling.

Deoxynivalenol inhibits proliferation and induces apoptosis in human umbilical vein endothelial cells

Deoxynivalenol (DON) is a stable mycotoxins found in cereals infected by certain fungal species and causes adverse health effects in animals and human such as vomiting, diarrhea and reproductive toxicity. In this study, we investigated the toxic and apoptotic effects of DON in human umbilical vein endothelial cells (HUVECs), a good model for studying inflammation. The results show that DON significantly inhibited the viability of HUVECs. DON could also inhibit the proliferation of HUVECs through G2/M phase arrest in cell cycle progression. Moreover, oxidative stress induced by DON was indicated by observations of increased levels of reactive oxygen species (ROS). In addition, DON also causes mitochondrial damage by decreasing the mitochondrial membrane potential and inducing apoptosis by up-regulation of apoptosis-related genes like caspase-3, caspase-9, and Bax genes, and down-regulation of Bcl-2 gene. These results together suggest that DON could induce cell cycle arrest, oxidative stress, and apoptosis in HUVECs.

Reduced susceptibility to Fusarium head blight in Brachypodium distachyon through priming with the Fusarium mycotoxin deoxynivalenol

The fungal cereal pathogen Fusarium graminearum produces deoxynivalenol (DON) during infection. The mycotoxin DON is associated with Fusarium head blight (FHB), a disease that can cause vast grain losses. Whilst investigating the suitability of Brachypodium distachyon as a model for spreading resistance to F. graminearum, we unexpectedly discovered that DON pretreatment of spikelets could reduce susceptibility to FHB in this model grass. We started to analyse the cell wall changes in spikelets after infection with F. graminearum wild-type and defined mutants: the DON-deficient Δtri5 mutant and the DON-producing lipase disruption mutant Δfgl1, both infecting only directly inoculated florets, and the mitogen-activated protein (MAP) kinase disruption mutant Δgpmk1, with strongly decreased virulence but intact DON production. At 14 days post-inoculation, the glucose amounts in the non-cellulosic cell wall fraction were only increased in spikelets infected with the DON-producing strains wild-type, Δfgl1 and Δgpmk1. Hence, we tested for DON-induced cell wall changes in B. distachyon, which were most prominent at DON concentrations ranging from 1 to 100 ppb. To test the involvement of DON in defence priming, we pretreated spikelets with DON at a concentration of 1 ppm prior to F. graminearum wild-type infection, which significantly reduced FHB disease symptoms. The analysis of cell wall composition and plant defence-related gene expression after DON pretreatment and fungal infection suggested that DON-induced priming of the spikelet tissue contributed to the reduced susceptibility to FHB.

Deoxynivalenol (Vomitoxin)-Induced Cholecystokinin and Glucagon-Like Peptide-1 Release in the STC-1 Enteroendocrine Cell Model Is Mediated by Calcium-Sensing Receptor and Transient Receptor Potential Ankyrin-1 Channel

Food refusal is a hallmark of exposure of experimental animals to the trichothecene mycotoxin deoxynivalenol (DON), a common foodborne contaminant. Although studies in the mouse suggest that DON suppresses food intake by aberrantly inducing the release of satiety hormones from enteroendocrine cells (EECs) found in the gut epithelium, the underlying mechanisms for this effect are not understood. To address this gap, we employed the murine neuroendocrine tumor STC-1 cell line, a widely used EEC model, to test the hypothesis that DON-induced hormone exocytosis is mediated by G protein-coupled receptor (GPCR)-mediated Ca(2+) signaling. The results indicate for the first time that DON elicits Ca(2)-dependent secretion of cholecystokinin (CCK) and glucagon-like peptide-1(7-36) amide (GLP-1), hormones that regulate food intake and energy homeostasis and that are products of 2 critical EEC populations--I cells of the small intestine and L cells of the large intestine, respectively. Furthermore, these effects were mediated by the GPCR Ca(2+)-sensing receptor (CaSR) and involved the following serial events: (1)PLC-mediated activation of the IP3 receptor and mobilization of intracellular Ca(2+) stores, (2) activation of transient receptor potential melastatin-5 ion channel and resultant L-type voltage-sensitive Ca(2+) channel-facilitated extracellular Ca(2+) entry, (3) amplification of extracellular Ca(2+) entry by transient receptor potential ankyrin-1 channel activation, and finally (4) Ca(2+)-driven CCK and GLP-1 excytosis. These in vitro findings provide a foundation for future investigation of mechanisms by which DON and other trichothecenes modulate EEC function in ex vivo and in vivo models.

Deoxynivalenol induces apoptosis in chicken splenic lymphocytes via the reactive oxygen species-mediated mitochondrial pathway

We investigated the immunotoxicity and cytotoxicity of deoxynivalenol (DON), a mycotoxin, and the mechanism by which it induces apoptosis. Chicken splenic lymphocytes treated with 0-50μg/mL DON for 48h inhibited growth of splenic lymphocytes in a dose-dependent manner, as revealed by the Cell Counting Kit-8 (CCK-8) bioassay. Annexin V-fluorescein isothiocyanate staining indicated that the number of apoptotic and necrotic cells were significantly higher compared with the control (P<0.01). DON treatment induced ROS accumulation, resulting in reduced mitochondrial transmembrane potential, as detected by flow cytometry and 2',7'-dichlorofluorescein acetate and rhodamine 123 labeling, respectively. Enzyme linked immunosorbent assays revealed that the concentrations of p53, Bax, Bak-1, and Caspase-3 increased with increasing DON concentration (P<0.05 or P<0.01), whereas the concentrations of Bcl-2 decreased (P<0.01) compared with the control. These data suggest that DON induces apoptosis in splenic lymphocytes via a ROS-mediated mitochondrial pathway.

Crosstalk of JNK1-STAT3 is critical for RAW264.7 cell survival

T-2 toxin, a major compound of trichothecenes, inhibits protein synthesis and induces inflammation and cell apoptosis through the activation of MAPK pathway. The JAK/STAT pathway has recently been shown to be downstream targets of trichothecenes. However, whether there is any crosstalk between JNK and JAK/STAT pathways in trichothecene toxicity has not been studied. In the present study, we explored this potential in RAW264.7 cells treated with T-2 toxin. Our results revealed a crosstalk between JNK1 and STAT3 after T-2 toxin treatment, which was mediated by K-Ras. T-2 toxin treatment resulted in rapid phosphorylation, and more importantly, JNK1-STAT3 signaling pathway was shown to maintain the normal function of the mitochondria and to inhibit T-2 toxin-induced apoptosis. Therefore, this pathway was considered to be a potential cell survival pathway. Breakdown and degranulation of ribosomes in the rough endoplasmic reticulum and swelling of mitochondria were clearly visible after the cells had been incubated with T-2 toxin for 12h. Our data suggest that T-2 toxin had a Janus face: it induced both apoptotic and cell survival pathways. These results suggest that the crosstalk and the balance between MAPK and JAK/STAT pathway might be involved in T-2 toxin-induced apoptosis in RAW264.7 cells.

PknE, a serine/threonine protein kinase of Mycobacterium tuberculosis initiates survival crosstalk that also impacts HIV coinfection

Serine threonine protein kinases (STPK) play a major role in the pathogenesis of Mycobacterium tuberculosis. Here, we examined the role of STPK pknE, using a deletion mutant ΔpknE in the modulation of intracellular signaling events that favor M. tuberculosis survival. Phosphorylation kinetics of MAPK (p38MAPK, Erk½ and SAPK/JNK) was defective in ΔpknE compared to wild-type infected macrophages. This defective signaling dramatically delayed and reduced the phosphorylation kinetics of transcription factors ATF-2 and c-JUN in ΔpknE infected macrophages. MAPK inhibitors instead of reducing the phosphorylation in ΔpknE infected macrophages, revealed crosstalks with Erk½ signaling influenced by SAPK/JNK and p38 pathways independently. Modulations in intra cellular signaling altered the expression of coreceptors CCR5 and CXCR4 in ΔpknE infected macrophages. In conclusion, pknE plays a role in MAPK crosstalks that enables intracellular survival of M. tuberculosis. This survival strategy also impacts HIV/TB coinfection.

Evaluation of deoxynivalenol-induced toxic effects on DF-1 cells in vitro: cell-cycle arrest, oxidative stress, and apoptosis

Deoxynivalenol (DON) is one of the most common mycotoxin contaminants of raw and processed cereal food. Lymphoid cells and fibroblasts are specified to be the most DON-sensitive cell types. In this study, we investigated the toxic effects of DON in chicken embryo fibroblast DF-1 cells. The results showed that DON significantly inhibited DF-1 cell viability in both a time- and concentration-dependent manner. DON could also inhibit the proliferation of DF-1 cells through G2/M phase arrest in the cell cycle progression. Moreover, oxidative stress induced by DON was indicated by increased levels of reactive oxygen species (ROS), malondialdehyde (MDA), and decreased levels of glutathione (GSH) and superoxide dismutase (SOD). In addition, DON could also cause mitochondrial damage by decreasing the mitochondrial membrane potential and induce apoptosis accompanied with the up-regulation of apoptosis-related genes including Caspase-3, Caspase-8, Caspase-9, and AIFM1. These results suggested that DON could cause cell cycle arrest, oxidative stress, and apoptosis in DF-1 cells.

Deoxynivalenol affects the composition of the basement membrane proteins and influences en route the migration of CD16(+) cells into the intestinal epithelium

The numerous pores in the basement membrane (BM) of the intestinal villi are essential for the communication of enterocytes with cells in the lamina propria, an important mechanism for the induction of intestinal immune responses. The intestinal epithelial barrier is affected by the mycotoxin deoxynivalenol (DON) from both the apical (luminal) and basolateral (serosal) side. The pig is the most susceptible species to the anorectic and immune-modulating effects of DON, which is most prevalent in crops. We analysed in pigs the effect of DON-contaminated feed on the composition and perforation of the BM and the presence of CD16⁺ cells or their dendrites in the epithelium. In addition to in vivo experiments, in vitro studies were carried out. Using microarray analyses, the effects of DON on IPEC-J2 cells were studied with the focus on the BM. Our in vivo results showed in the control pigs: (1) a significant increased pore number (p ≤ 0.001) in the jejunum in comparison to ileum, (2) no difference in the pore size, and (3) comparable frequency of intraepithelial CD16⁺ cells/dendrites in the jejunum and ileum. There was a marked trend that DON feeding increases: (1) the pore number in jejunum, and (2) the number of CD16⁺ cells/dendrites in the epithelium (Tukey–Kramer; p = 0.055 and p = 0.067, respectively). The in vivo results were extended with microarray analyses of epithelial cell (IPEC-J2 cells). The down-regulation of genes like syndecan, fibulin 6 and BM-40 was observed. These proteins are important factors in the BM composition and in formation of pores. Our results provide evidence that already low basolateral concentrations of DON (50 ng/mL) influence the production of the BM protein laminin by epithelial cells. Thus, DON affects the composition of the BM.

Early phosphoproteomic changes in the mouse spleen during deoxynivalenol-induced ribotoxic stress

The trichothecene mycotoxin deoxynivalenol (DON) targets the innate immune system and is of public health significance because of its frequent presence in human and animal food. DON-induced proinflammatory gene expression and apoptosis in the lymphoid tissue have been associated with a ribotoxic stress response (RSR) that involves rapid phosphorylation of mitogen-activated protein kinases (MAPKs). To better understand the relationship between protein phosphorylation and DON's immunotoxic effects, stable isotope dimethyl labeling-based proteomics in conjunction with titanium dioxide chromatography was employed to quantitatively profile the immediate (≤ 30min) phosphoproteome changes in the spleens of mice orally exposed to 5mg/kg body weight DON. A total of 90 phosphoproteins indicative of novel phosphorylation events were significantly modulated by DON. In addition to critical branches and scaffolds of MAPK signaling being affected, DON exposure also altered phosphorylation of proteins that mediate phosphatidylinositol 3-kinase/AKT pathways. Gene ontology analysis revealed that DON exposure affected biological processes such as cytoskeleton organization, regulation of apoptosis, and lymphocyte activation and development, which likely contribute to immune dysregulation associated with DON-induced RSR. Consistent with these findings, DON impacted phosphorylation of proteins within diverse immune cell populations, including monocytes, macrophages, T cells, B cells, dendritic cells, and mast cells. Fuzzy c-means clustering analysis further indicated that DON evoked several distinctive temporal profiles of regulated phosphopeptides. Overall, the findings from this investigation can serve as a template for future focused exploration and modeling of cellular responses associated with the immunotoxicity evoked by DON and other ribotoxins.

Alternariol induces abnormal nuclear morphology and cell cycle arrest in murine RAW 264.7 macrophages

The mycotoxin alternariol (AOH), a frequent contaminant in fruit and cereal products, is known to induce DNA damage with subsequent cell cycle arrest. Here we elucidated the effects of AOH on stages of cell cycle progression using the RAW 264.7 macrophage model. AOH resulted in an accumulation of cells in the G2/M-phase (4N). Most cells exhibited a large G2 nucleus whereas numbers of true mitotic cells were reduced relative to control. Both cyclin B1 and p-cdc2 levels increased, while cyclin B1 remained in the cytoplasm; suggesting arrest in the G2/M transition point. Remarkably, after exposure to AOH for 24h, most of the cells exhibited abnormally shaped nuclei, as evidenced by partly divided nuclei, nuclear blebs, polyploidy and micronuclei (MN). AOH treatment also induced abnormal Aurora B bridges, suggesting that cytokinesis was interfered within cells undergoing karyokinesis. A minor part of the resultant G1 tetraploid (4N) cells re-entered the S-phase and progressed to 8N cells.

Deoxynivalenol impairs the immune functions of neutrophils

SCOPE

Deoxynivalenol (DON), a mycotoxin produced by Fusarium spp., is toxic to many animal species, with pigs being the most sensitive species to the toxin. The aim of the present study was to determine the effects of DON on pig polymorphonuclear cells (PMNs), the first line of defense against infection.

METHODS AND RESULTS

PMNs isolated from pig blood samples were stimulated with LPS to mimic infection. DON (0.5-10 μM) altered three main functions of pig PMNs: LPS-induced secretion of IL-8, chemotaxis, and phagocytosis capability. This alteration of PMN properties was due to apoptotis induced by DON exposure. Using Western blot and flow cytometry, we demonstrated that this process included the permeabilization of the mitochondrial outer membrane and the activation of caspase-3. The effect of DON was mediated by the phosphorylation of the p38 mitogen-activated protein kinase within the first 30 min of exposure.

CONCLUSION

This study provides evidence that low concentrations of DON can alter the immune functions of porcine PMNs and suggests the involvement of p38 mitogen-activated protein kinase in the signal transduction pathway. These immunosuppressive effects of DON may have implications for humans and/or animals when eating contaminated food/feed.

The food contaminant deoxynivalenol activates the mitogen activated protein kinases in the intestine: interest of ex vivo models as an alternative to in vivo experiments

Trichothecenes induce changes in the intestinal barrier function through decreased expression of cell junction proteins and apoptosis of enterocytes. The mitogen activated protein kinases (MAPK) play an important role in the signaling pathways of cell turnover and differentiation. Using ex vivo and in vivo approaches, the purpose of this study was to investigate the ability of low doses of DON to induce histological changes in the intestine and to activate the MAPK ERK 1/2, p38 and JNK. Twelve weaning piglets received during four weeks a control diet or a DON-contaminated diet (2.3 mg DON/kg feed). Six weaning piglets were used to prepare jejunal explants (ex vivo model). Explants were exposed during 4 h to vehicle, 5 or 10 μM DON. Intestinal changes were graded using a histological score. Pigs fed a DON-diet and explants exposed to DON showed a significant decrease in the jejunal score. In both models, the toxin significantly enhanced phosphorylation of ERK 1/2 and p38, whereas the increased phosphorylation of JNK was non significant. Taken together these results indicate that in vivo or ex vivo exposure of intestinal tissue to DON lead to similar intestinal lesions and activation of MAPK. These effects could impair the homeostasis of intestinal tissue in the aspects of barrier function and immune protection. The similarity of the in vivo and ex vivo results provides also strong evidence that the jejunal explant model is a good alternative for toxicological studies in intestinal tissue.

Global protein phosphorylation dynamics during deoxynivalenol-induced ribotoxic stress response in the macrophage

Deoxynivalenol (DON), a trichothecene mycotoxin produced by Fusarium that commonly contaminates food, is capable of activating mononuclear phagocytes of the innate immune system via a process termed the ribotoxic stress response (RSR). To encapture global signaling events mediating RSR, we quantified the early temporal (≤30min) phosphoproteome changes that occurred in RAW 264.7 murine macrophage during exposure to a toxicologically relevant concentration of DON (250ng/mL). Large-scale phosphoproteomic analysis employing stable isotope labeling of amino acids in cell culture (SILAC) in conjunction with titanium dioxide chromatography revealed that DON significantly upregulated or downregulated phosphorylation of 188 proteins at both known and yet-to-be functionally characterized phosphosites. DON-induced RSR is extremely complex and goes far beyond its prior known capacity to inhibit translation and activate MAPKs. Transcriptional regulation was the main target during early DON-induced RSR, covering over 20% of the altered phosphoproteins as indicated by Gene Ontology annotation and including transcription factors/cofactors and epigenetic modulators. Other biological processes impacted included cell cycle, RNA processing, translation, ribosome biogenesis, monocyte differentiation and cytoskeleton organization. Some of these processes could be mediated by signaling networks involving MAPK-, NFκB-, AKT- and AMPK-linked pathways. Fuzzy c-means clustering revealed that DON-regulated phosphosites could be discretely classified with regard to the kinetics of phosphorylation/dephosphorylation. The cellular response networks identified provide a template for further exploration of the mechanisms of trichothecenemycotoxins and other ribotoxins, and ultimately, could contribute to improved mechanism-based human health risk assessment.

Mechanisms for ribotoxin-induced ribosomal RNA cleavage

The Type B trichothecene deoxynivalenol (DON), a ribotoxic mycotoxin known to contaminate cereal-based foods, induces ribosomal RNA (rRNA) cleavage in the macrophage via p38-directed activation of caspases. Here we employed the RAW 264.7 murine macrophage model to test the hypothesis that this rRNA cleavage pathway is similarly induced by other ribotoxins. Capillary electrophoresis confirmed that the antibiotic anisomycin (≥25ng/ml), the macrocylic trichothecene satratoxin G (SG) (≥10ng/ml) and ribosome-inactivating protein ricin (≥300ng/ml) induced 18s and 28s rRNA fragmentation patterns identical to that observed for DON. Also, as found for DON, inhibition of p38, double-stranded RNA-activated kinase (PKR) and hematopoietic cell kinase (Hck) suppressed MAPK anisomycin-induced rRNA cleavage, while, in contrast, their inhibition did not affect SG- and ricin-induced rRNA fragmentation. The p53 inhibitor pifithrin-μ and pan caspase inhibitor Z-VAD-FMK suppressed rRNA cleavage induced by anisomycin, SG and ricin, indicating that these ribotoxins shared with DON a conserved downstream pathway. Activation of caspases 8, 9 and 3 concurrently with apoptosis further suggested that rRNA cleavage occurred in parallel with both extrinsic and intrinsic pathways of programmed cell death. When specific inhibitors of cathepsins L and B (lysosomal cysteine cathepsins active at cytosolic neutral pH) were tested, only the former impaired anisomycin-, SG-, ricin- and DON-induced rRNA cleavage. Taken together, the data suggest that (1) all four ribotoxins induced p53-dependent rRNA cleavage via activation of cathepsin L and caspase 3, and (2) activation of p53 by DON and anisomycin involved p38 whereas SG and ricin activated p53 by an alternative mechanism.

Immune modulatory effects of the foodborne contaminant citrinin in mice

The mycotoxin citrinin can cause mycotoxic nephropathy, cytotoxicity and genotoxicity. To investigate the immune modulatory effects, CTN was orally administered to female BALB/c mice at the dose of 1, 5, or 10 mg/kg body weight for 14 days, and several immunotoxicity tests were performed. The populations of F4/80+ cells and CD19+ cells were significantly decreased in spleen and MLN. In MLN, CD4+, CD8+, and CD4+CD25+Foxp3+ cell populations were increased. CD8+ cells were increased but CD19+ cells were decreased in intra-epithelial, lamina propria and Peyer's patches lymphocytes. In a cell proliferation assay, along with the increased proliferative capacities of ConA-induced splenocytes and MLN cells, IFN-γ production was increased. The expression of TLR 2 was increased in spleen, but TLR 3 expression in MLN was decreased. The level of serum IgM was reduced. Furthermore, apoptosis was induced in spleen, MLN and Peyer's patches and promoted by the change in the ratio of Bax/Bcl-2 activities. Autophagy gene Atg5 and Beclin-1 were up-regulated in spleen. The expressions of IL-1β, IL-10, and TNF-α were inhibited in murine macrophage cells pre-exposed with TLR ligands. These results indicate that CTN has multiple immune modulatory effects in mice that may alter normal functions of immune system.

Targets and intracellular signaling mechanisms for deoxynivalenol-induced ribosomal RNA cleavage

The trichothecene mycotoxin deoxynivalenol (DON), a known translational inhibitor, induces ribosomal RNA (rRNA) cleavage. Here, we characterized this process relative to (1) specific 18S and 28S ribosomal RNA cleavage sites and (2) identity of specific upstream signaling elements in this pathway. Capillary electrophoresis indicated that DON at concentrations as low as 200 ng/ml evoked selective rRNA cleavage after 6 h and that 1000 ng/ml caused cleavage within 2 h. Northern blot analysis revealed that DON exposure induced six rRNA cleavage fragments from 28S rRNA and five fragments from 18S rRNA. When selective kinase inhibitors were used to identify potential upstream signals, RNA-activated protein kinase (PKR), hematopoietic cell kinase (Hck), and p38 were found to be required for rRNA cleavage, whereas c-Jun N-terminal kinase and extracellular signal-regulated kinase were not. Furthermore, rRNA fragmentation was suppressed by the p53 inhibitors pifithrin-α and pifithrin-μ as well as the pan caspase inhibitor Z-VAD-FMK. Concurrent apoptosis was confirmed by acridine orange/ethidium bromide staining and flow cytometry. DON activated caspases 3, 8, and 9, thus suggesting the possible coinvolvement of both extrinsic and intrinsic apoptotic pathways in rRNA cleavage. Satratoxin G (SG), anisomycin, and ricin also induced specific rRNA cleavage profiles identical to those of DON, suggesting that ribotoxins might share a conserved rRNA cleavage mechanism. Taken together, DON-induced rRNA cleavage is likely to be closely linked to apoptosis activation and appears to involve the sequential activation of PKR/Hck →p38→p53→caspase 8/9→caspase 3.